Mortar shells, artillery shells and other such explosive projectiles normally have a safing and arming device which operates to allow detonation of the explosive only after the projectile has been fired or launched. Often, the safing and arming circuit will comprise a switching device which responds to a "signature" or force due to firing, such as the setback acceleration or the spin of the projectile. It is essential that such a switching device responds only upon firing of the projectile and not react to impacts due to mishandling of the explosive shell. Switches known in the prior art which meet this need are generally complex gas- or liquid-damped designs or clockworks which are costly and require precision assembly of parts.
U.S. Pat. No. 4,284,862 shows an acceleration-actuated switch capable of distinguishing between random and brief acceleration forces on the one hand and sustained acceleration forces on the other hand. This device comprises a stationary electrical contact and a movable contact held in position by biasing means. Sustained acceleration forces in a particular direction will drive the movable contact along a fixed path to a position whereat the movable contact comes into proximity with the stationary contact thereby closing the switch. If the acceleration force is not in the proper direction or magnitude or is not applied to the switch for a sufficient length of time, the biasing means will return the movable contact to its original position thereby maintaining the switch in an open condition.
U.S. Pat. No. 4,814,381 shows an inertial arm/disarm switch having an inertial mass, a shaft with a zig zag channel, a gearless electric motor, a switch deck and blocking rotor, another blocking rotor, and a spring which provides a restoring force which acts against the inertia of the inertial mass. In this device, the blocking rotors have notches which interface with the associated inertial mass or masses and lock the rotors against rotative movement unless the inertial masses are in the proper positions.
The above cited prior art mechanical safe and arm devices all consist of three-dimensional zig zag delay devices on the scale of millimeters or centimeters, fashioned by precision machining, casting, or other such "macro" means to serve the purpose of providing a mechanical delay before closing a switch, or removing a detent on a detonator slider in a fuze S & A. To fabricate these devices is costly in that these devices are required to be extremely precision components often requiring time-consuming sorting of components, which limits the use of these types of devices.
In recent years, the LIGA technique has evolved as a basic fabrication process for the production of a large variety of microstructure products utilizing metals, polymers, ceramics and even glasses. The extreme precision of the microstructure products, their large aspect ratios for height vs. lateral dimension in combination with an inexpensive replication process opens a broad field of application for the fabrication of sensors, actuators, micromechanical components, microoptical systems, electrical and optical microconnectors. Deep X-ray lithography is the most important fabrication step in the sequence of the LIGA technique. It provides a three-dimensional master microstructure based on a radiation sensitive polymer material, which in general is reproduced in subsequent electroforming and molding processes.